Basic Features of the Crustal Structure in the Lower Yangtze and Its Neighboring Area in the Chinese Mainland： Review of Deep Seismic Sounding Research  

作　　者：Bai Zhiming Wu Qingju Xu Tao Wang Xiao 

机构地区：[1]State Key Laboratory of Lithosphere Evolution, Institute of Geology and Geophysics, CAS, Beijing 100029, China [2]Institute of Geophysics, China Earthquake Administration, Beijing 100081, China [3]CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China [4]University of Chinese Academy of Sciences, Beijing 100049, China

出　　处：《Earthquake Research in China》2016年第3期298-315,共18页中国地震研究（英文版）

基　　金：funded by the Special Public Welfare Industry Research of China Earthquake Administration(201408023);Academician Chen Yong Workstation Special Funds of Yunnan Province and Natural Science Foundation of China(41374062,41174075)

摘　　要：The Deep Seismic Sounding( DSS) projects carried out from the 1970 s in the lower Yangtze region and its neighboring area were reviewed in this paper,then the basic wave group features of those wide angle reflection / refraction record sections,and of the crustal structure are summarized. It shows that there were in total five clear wave groups on the record sections,which include the first arrival Pg,the reflection P1 from the bottom interface of the upper crust,the reflection P3 from the bottom interface of the middle crust,the strong reflection Pm from the Moho boundary,and the refraction Pn from uppermost mantle. In general,these phases are easily consistently traced and compared,despite some first arrivals being delayed or arriving earlier than normal due to the shallow sedimentary cover or bedrocks. In particular,in the Dabie Mountain region the seismic events of a few gathered shots always have weak reflection energy,are twisted,or exhibit disorganized waveforms, which could be attributed to the disruption variations of reflection depth,the broken Moho,and the discontinuity of the reflection boundary within crust. The regional crustal structures are composed of the upper,middle and lower crust,of which the middle and lower layers can be divided into two weak reflection ones. The crustal thickness of the North China and Yangtze platform are 30km- 36 km,and the Moho exhibits a flat geometry despite some local uplifts. The average pressure velocity in lower crust beneath this two tectonic area is 6. 7 ± 0. 3km / s. Nevertheless,beneath the Dabieshan area the crustal thickness is 32km- 41 km,the Moho bends down sharply andtakes an abrupt 4km- 7km dislocation in the vertical direction. The average pressure velocity in the lower crust beneath the Dabieshan area is 6. 8 ± 0. 2km / s.The Deep Seismic Sounding （DSS） projects carried out from the 1970s in the lower Yangtze region and its neighboring area were reviewed in this paper, then the basic wave group features of those wide angle reflection/refraction record sections, and of the crustal structure are summarized. It shows that there were in total five clear wave groups on the record sections, which include the first arrival Pg, the reflection P1 from the bottom interface of the upper crust, the reflection P3 from the bottom interface of the middle crust, the strong reflection Pm from the Moho boundary, and the refraction Pn from uppermost mantle. In general, these phases are easily consistently traced and compared, despite some first arrivals being delayed or arriving earlier than normal due to the shallow sedimentary cover or bedrocks. In particular, in the Dabie Mountain region the seismic events of a few gathered shots always have weak reflection energy, are twisted, or exhibit disorganized waveforms, which could be attributed to the disruption variations of reflection depth, the broken Moho, and the discontinuity of the reflection boundary within crust. The regional crustal structures are composed of the upper, middle and lower crust, of which the middle and lower layers can be divided into two weak reflection ones. The crustal thickness of the North China and Yangtze platform are 30kin -36km, and the Moho exhibits a flat geometry despite some local uplifts. The average pressure velocity in lower crust beneath this two tectonic area is 6. 7 ± 0. 3km/s. Nevertheless, beneath the Dabieshan area the crustal thickness is 32km -41km, the Moho bends down sharply and takes an abrupt 4km -7km dislocation in the vertical direction. The average pressure velocity in the lower crust beneath the Dabieshan area is 6. 8±0. 2km/s.

关 键 词：Deep seismic sounding projects Wave group feature Crustal structure feature Anhui Province and its neighboring area 

分 类 号：P631.4[天文地球—地质矿产勘探]